Linux+ Hardware Part 08 – Expansion Slots

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  1. Jarret W. Buse

    Jarret W. Buse Active Member Staff Writer

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    Linux+ Hardware Part 08 – Expansion Slots

    In a previous Linux+ article, I stated that expansion cards help increase the functionality of a Personal Computer (PC). For example, a server could include a Fax/Modem card which would allow the server to be a Fax Server.

    Expansion cards allow systems to offer a wider range of functionality without having to buy a system with all the required built-in devices. Even if you purchase a system with a built-in video card, one that is physically on the motherboard, you can add a better video card to an expansion slot.

    NOTE: Expansion slots exist on desktop style systems and require the cover to be removed to install the card. Laptops offer a slot to allow a card to be inserted and removed without taking the system apart.

    There are seven expansion slot types:
    1. Industry Standard Architecture (ISA)
    2. Extended Industry Standard Architecture (EISA)
    3. Micro Channel Architecture (MCA)
    4. Peripheral Component Interconnect (PCI)
    5. Video Electronics Standard Association (VESA)
    6. Accelerated Graphics Port (AGP)
    7. PC Card or Personal Computer Memory Card International Association (PCMCIA)
    Industry Standard Architecture (ISA)

    ISA was introduced in the 1980’s as an 8-bit card slot. Later, when 16-bit systems were introduced, the ISA slot was extended to include another set of connectors allowing for 16-bit cards to be used.

    Hardware 8 - Picture 1.JPG
    PICTURE 1

    In 1993, ISA was modified to include Plug-and-Play (PnP) capabilities. PnP allowed the resources for a card to be automatically configured.

    NOTE: The cards must be PnP compatible. Cards which are not PnP compatible are called Legacy Cards.

    PnP managers within the Operating System (OS) handle the configuration of the resources needed by the card. The resources are determined by a Read Only Memory (ROM) chip on the card itself.

    Extended Industry Standard Architecture (EISA)

    EISA was an extension of the original ISA to support 32-bit systems. Expansion cards could now be 32-bit as well. EISA included Bus Mastering for enhanced throughput.

    EISA slots had an extra section of connectors to allow the EISA cards to connect at 32-bit. Of course, only EISA cards could fit into an EISA slot.

    Hardware 8 - Picture 2.JPG
    PICTURE 2

    EISA included a form of PnP which allowed EISA software to configure the EISA cards automatically.

    NOTE: Linux does not support EISA, but you should know that it does exist.

    Micro Channel Architecture (MCA)

    The MCA slots were 32-bit in size, but are smaller in length than the EISA slots.

    Hardware 8 - Picture 3.JPG
    PICTURE 3

    The MCA slots offered a Bus Mastering style of communications called Central Arbitration Point (CAP). CAP allowed the CPU to complete its processing while the cards use the Data and Address Buses. MCA also uses Burst Mode to transmit blocks of data.

    The MCA Bus slots were incompatible with ISA cards, so cards could not be moved from an older system.

    Peripheral Component Interconnect (PCI)

    PCI was one of the Local Bus architectures. The Local Bus is when the expansion slots are connected directly to the CPU, has the same size data paths as the CPU and operates at the same speed as the CPU. PCI offers both 32-bit and 64-bit card support with PnP support.

    Hardware 8 - Picture 4.JPG
    PICTURE 4

    PCI supports burst mode for data transfers. For 64-bit PCI cards, data transfers can be as much as 533 MB/s.

    Video Electronics Standard Association (VESA)

    VESA is the second Local Bus architecture. VESA offers a 32-bit data path to the CPU.

    NOTE: VESA can sometimes be referred to as VESA Local Bus (VLB).

    Hardware 8 - Picture 5.JPG
    PICTURE 5

    VESA offers Burst Mode for data transfers and Bus Mastering.

    NOTE: A system could only handle three VESA slots since only three cards could be used at once. The limitation is due to the electrical charge of the CPU which can be insufficient to sometimes even handle three cards.

    Accelerated Graphics Port (AGP)

    AGP is based off of PCI to support high speed graphics. AGP cards appear similar to PCI, but are mounted offset to the PCI slots.

    Hardware 8 - Picture 6.JPG
    PICTURE 6

    In the picture the blue slot is a PCI slot. The AGP slot is the orange slot and is offset more to the side.

    The AGP slot has a direct connection to RAM to allow faster throughput.

    AGP has multiple specifications, such as 1.0 and 2.0. Specification 1.0 includes AGP 1x and 2x. Specification 2.0 includes AGP 4x. If an AGP 4x card is placed into an AGP 1.0 slot, the card will operate as if it were 2x. AGP specification 8.0 offers support for AGP 8x.

    PC Card or Personal Computer Memory Card International Association (PCMCIA)

    The last type of expansion card is for portable systems. These cards are called PC Cards or Personal Computer Memory Card International Association (PCMCIA) cards. The cards come in Type I, II, and III, the common type being Type II.

    The Type I card is the smallest, Type II is a little larger and Type III is the largest. The actual sizes are: Type I is 3.3 mm thick, Type II is 5.5 mm thick and Type III is 10.5 mm thick.


    PC Cards are hot-swappable, meaning that the card can be removed while the system is powered on and another inserted in its place. This is similar to the Universal Serial Bus (USB).

    PC Cards are 16-bit, so to support 32-bits the CardBus was introduced which still allowed for backwards compatibility to use the 16-bit cards.

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